Railroad crossings are often the scenes of tragic accidents when car drivers, cyclists or pedestrians underestimate the danger at these junctions. Worldwide, accidents at railroad crossings lead to thousands of casualties every year, and above all, at unsecured crossings. Http://www.rail-reg.gov.uk/upload/pdf/railsafety0304.pdf from Office of Rail Regulation in the UK shows that the Great Britain railway network alone had 18 deaths of members of the public in 2004, 17 of which happened at non-secured level crossings.
Manual detection and warning is the most widely used method when railway track maintenance has to be performed on tracks that are operated by trains. Usually one or more of the maintenance workers have to supervise the track at a remote location relative the maintenance location, and call their colleagues at work if a train should appear.
A number of systems for detecting a train at a specific location have been developed. In such systems the train is detected when it passes a sensor, and the output sensor signal is used to trigger a warning system or an automatic level crossing gate. The sensor may communicate with the warning system or automatic level crossing by cable or radio signals.
U.S. Pat. No. 5,924,651 shows a warning system and method for warning personnel in proximity to railroad tracks of an approaching train. A transmitter for transmitting a warning signal in response to a train sensor detecting passage of a train over the railroad tracks at a given location is used.
Early detection of remote trains by listening on the rails was known by the American Indians. By listening over a certain time period the Indians were able to determine whether the train was approaching or departing.
U.S. Pat. No. 5,265,831 describes a method and apparatus for detecting an impact sound by an impact sound receiver, such as a sound caused by a railroad vehicle approaching a specific location, and if the intensity of the output from the sound receiver is above a certain level, a minimum time, a warning signal is triggered.